Credit: X-ray: NASA/CXC/SAO/Univ Mexico/S. Estrada-Dorado et al.; Ultraviolet: NASA/JPL; Optical: NASA/ESA/STScI (M. Meixner)/NRAO (T.A. Rector); Infrared: ESO/VISTA/J. Emerson; Image Processing: NASA/CXC/SAO/K. Arcand; Illustration: NASA/CXC/SAO/M. Weiss
Remains of a Planet in a Planetary Nebula?
When stars like our Sun run out of their thermonuclear fuel, they begin to expand, and eventually they shed their outer layers into space. These lost outer layers often form beautiful, complicated bubbles in space, light-years in size. These bubbles are called "planetary nebulae" - a typical astronomical misnomer, since the material is not directly connected to planets or planetary systems. The central core of the star remains behind as a compact object called a "white dwarf" (another misnomer). White dwarfs are incredibly dense; they contain nearly as much mass as the Sun, compressed into a ball the size of the earth. White dwarfs are so dense that a teaspoonful would contain as much mass as pickup truck. One of the prettiest planetary nebulae is the well-know Helix Nebula, shown above. The Helix is a nearly spherical shell of gas and dust, which appears as a circle on the sky, with knots, streamers, and other outer structures visible, tracing the complicated history of how the star lost its outer layers. The white dwarf star is also visible in the image above as a faint point of light near the center of the Helix. At the heart of the Helix lies a mystery: unlike most other white dwarfs, the white dwarf in the Helix Nebula emits X-rays. New X-ray measurements with the Chandra X-ray Observatory and with the XMM-Newton X-ray telescope suggest that the X-ray emission may be produced by accretion of material onto the surface of the white dwarf, and conversion of the kinetic energy of the infalling material into X-rays as the material falls down onto the star. The origin of this material is uncertain, but the new analysis suggests we may be witnessing the disruption of a Jupiter-sized planet that wandered too close to the white dwarf and was torn apart by the white dwarf's powerful gravitational pull.
Published: March 24, 2025
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Page Author: Dr. Michael F. Corcoran
Last modified Monday, 24-Mar-2025 12:00:35 EDT